Patent application title: DEVICE AND METHOD FOR DETERMINING A MAPPING OF THE TORQUE TRANSMITTED BY A CLUTCH IN AN AUTOMOBILE AND HILL-START ASSISTANCE SYSTEM FOR AN AUTOMOBILE EQUIPPED WITH SUCH DEVICE

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DEVICE AND METHOD FOR DETERMINING A MAPPING OF THE TORQUE TRANSMITTED BY A CLUTCH IN AN AUTOMOBILE AND HILL-START ASSISTANCE SYSTEM FOR AN AUTOMOBILE EQUIPPED WITH SUCH DEVICE - Patent applicationinit();
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Patent application title: DEVICE AND METHOD FOR DETERMINING A MAPPING OF THE TORQUE TRANSMITTED BY A CLUTCH IN AN AUTOMOBILE AND HILL-START ASSISTANCE SYSTEM FOR AN AUTOMOBILE EQUIPPED WITH SUCH DEVICE

Abstract:

A device for determining, when driving a vehicle, a mapping of torque
transmitted by a clutch of the automobile based on a position of a clutch
control member. The device includes a mechanism updating the mapping
based on position thresholds of the clutch control member. The updating
modifies values of the thresholds based on minimum and maximum values of
the positions of the control member stored in the mapping and on current
values of the thresholds.

Claims:

1-9. (canceled)

10. A device for determining, while a vehicle is running, a mapping of
torque transmitted by a clutch fitted to the vehicle as a function of a
position of a clutch control member, the device comprising:updating means
for updating the mapping as a function of position thresholds of the
clutch control member,wherein the updating means comprises computing
means for modifying values of the thresholds as a function of minimum and
maximum values of positions of the clutch control member recorded in the
mapping, and of current value of the thresholds.

11. The device as claimed in claim 10, wherein the position thresholds
comprise a top threshold, a bottom threshold, and an intermediate
threshold.

12. The device as claimed in claim 10, wherein the updating means
comprises a counter of complete updates of the mapping.

13. The device as claimed in claim 12, wherein the updating means
comprises a comparator of the current value of the counter with a
predetermined value.

14. The device as claimed in claim 13, wherein the updating means is
configured to execute computing when the comparator determines that a
current value of the counter is equal to the predetermined value.

15. A system for assisting a hill start of a motor vehicle including a
device for determining a mapping of torque transmitted by a clutch as
claimed in claim 10, with a slope sensor and a controlled braking device,
comprising:means for controlling the braking device;means for estimating
the torque to be supplied by the clutch to overcome forces of gravity,
and a comparator of the torque to be supplied and of the torque supplied
by the clutch, available in the mapping.

16. The system as claimed in claim 15, wherein the means for controlling
the braking device is configured to control release of the brakes of the
braking device when the torque supplied by the clutch is greater than or
equal to the torque to be supplied to overcome the forces of gravity.

17. The system as claimed in claim 15, wherein the means for estimating
the torque to be supplied by the clutch to overcome the forces of gravity
is configured to compute the torque to be supplied based on the following
relation:CTd=r(b)ρwheelsmgsin(θtilt)in
which:CTd is the torque to be supplied by the clutch in order to
overcome the forces of gravity, in Nm;r(b) is the gearbox ratio
corresponding to the position b of the gearchange lever,
adimensional;ρwheels represents the radius of the wheels of the
vehicle, in m;m is the weight of the vehicle, in kg;g is the
gravitational field on the surface of the Earth, substantially equal to
9.81 ms-2; andθtilt is the inclination of the surface on
which the vehicle stands, supplied by the slope sensor, in rad.

18. A method for determining a mapping of torque transmitted by a clutch
fitted to a motor vehicle, as a function of a position of a clutch
control member,wherein, while the vehicle is running, the mapping is
updated based on position thresholds of the clutch control member,wherein
during the update, values of the thresholds are modified as a function of
minimum and maximum values of positions of the clutch control member
recorded in the mapping, and of current value of the thresholds.

Description:

[0001]The present invention relates to the field of driving assistance,
and in particular to starting the vehicle or setting it in motion.

[0002]The estimate of the clutch curve, or more precisely of a mapping of
the torque transmitted by a clutch fitted to a motor vehicle, can be of
use to various systems on board a motor vehicle, and in particular to a
system for assisting a hill start of a motor vehicle.

[0003]French patent application number 2 828 450 (Renault) relates to a
hill-start assistance device for a motor vehicle. The assistance device
comprises mainly a means for estimating a slope on which the vehicle is
positioned, a means for interpreting the actions of the driver, a means
for determining a characteristic curve of the clutch of the vehicle and a
means for automatically deactivating a braking means of the vehicle. The
motor vehicle can thus be held in position on a slope in a state in which
the drive wheels are disengaged from the engine, and can be set in motion
in the upslope direction only by the actions of the driver on the
accelerator and clutch pedals, without the driver having to act on the
parking brake. The assistance device controls the release of the brakes
as soon as the torque transmitted to the wheels is sufficient to
compensate for the force on the vehicle due to the slope and to gravity.

[0004]The mapping of the torque transmitted by a clutch fitted to a motor
vehicle is, in a conventional manner, updated, when the vehicle is in
motion, by means of predetermined and invariable position thresholds.

[0005]Therefore, an incorrect predetermination of these thresholds can
cause an incorrect update, and even an absence of an update, of the
mapping of the torque transmitted by the clutch.

[0006]Moreover, it is possible that the predetermined thresholds are
suitable for updating the mapping when the clutch is new, but become
unsuitable after a certain degree of wear of the clutch.

[0007]One object of the invention is to improve the accuracy of the update
of the mapping of the torque transmitted by the clutch with the wear of
the clutch.

[0008]Another object of the invention is to supply a hill-start assistance
system of a motor vehicle having an improved operating precision.

[0009]According to one aspect of the invention, a device is proposed for
determining, while a vehicle is running, a mapping of the torque
transmitted by a clutch fitted to the motor vehicle as a function of the
position of a clutch control member. The device comprises means for
updating said mapping as a function of position thresholds of the clutch
control member. The updating means comprise computing means for modifying
the values of said thresholds as a function of the minimum and maximum
values of the positions of the control member recorded in said mapping,
and of the current value of said thresholds.

[0010]Therefore, in addition to the fact that the clutch curve depends on
the thresholds, the thresholds also depend on the change in the clutch
curve. In other words, the clutch curve and the thresholds are
interdependent. The clutch control member may be a clutch pedal.

[0011]In one embodiment, the position thresholds comprise a top threshold,
a bottom threshold, and an intermediate threshold.

[0012]The position of the clutch control member, usually a clutch pedal,
can be defined as a percentage of the travel of the clutch pedal, with 0%
corresponding to the clutch pedal fully pushed in, that is to say the
clutch completely disengaged, and 100% corresponding to the clutch pedal
not pushed in or completely released, that is to say the clutch
completely engaged.

[0013]The top threshold corresponds to a position threshold of the clutch
pedal above which or for which the clutch is considered completely
engaged, for example 95%. The bottom threshold, for example 5%,
corresponds to the position threshold of the clutch pedal below which or
for which the clutch is considered completely disengaged. Moreover, an
intermediate threshold, for example 80%, is a value for which the clutch
is considered not completely engaged, and is used to identify the engaged
ratio of the gearbox. Therefore, when the position of the clutch pedal is
between the intermediate threshold and the top threshold, the state of
the clutch and the determined gearbox ratio depends on the previous state
of the clutch, through a phenomenon of hysteresis.

[0014]In one embodiment, said updating means comprise a counter of
complete updates of said mapping.

[0015]Therefore, it is possible, in a cyclical manner, after a
predetermined number of complete updates of the clutch mapping, to
recompute or update the position thresholds.

[0016]In one embodiment, said updating means comprise a comparator of the
current value of said counter with a predetermined value.

[0017]This predetermined value corresponds to the number of complete
updates of the mapping carried out successively before modifying the
position thresholds of the clutch pedal.

[0018]In one embodiment, the updating means are suitable for executing the
computing means when the comparator determines that the current value of
said counter is equal to said predetermined value.

[0019]According to another aspect of the invention, also proposed is a
system for assisting a hill start of a motor vehicle fitted with a device
for determining a mapping of the torque transmitted by a clutch as
described above, with a slope sensor and a controlled braking device. The
hill-start assistance system comprises means for controlling the braking
device comprising means for estimating the torque to be supplied by the
clutch in order to overcome the forces of gravity, and means for
comparing said torque to be supplied and the torque supplied by the
clutch available in said mapping.

[0020]Therefore, the hill-start assistance system has enhanced precision
notably because it takes account of the wear of the clutch.

[0021]In one embodiment, said means for controlling the braking device are
suitable for controlling the release of the brakes of the braking device
when the torque supplied by the clutch is greater than or equal to the
torque to be supplied in order to overcome the forces of gravity.

[0022]Therefore, during a hill start, the release of the brakes is managed
automatically by the vehicle, and the driver can occupy himself only with
the accelerator pedal and the clutch pedal, without worrying about the
parking brake.

[0023]In one embodiment, said means for estimating the torque to be
supplied by the clutch in order to overcome the forces of gravity are
suitable for computing said torque to be supplied based on the following
relation:

CTd=r(b)ρwheelsmgsin(θtilt)

in which: [0024]CTd is the torque to be supplied by the clutch in
order to overcome the forces of gravity, in Nm; [0025]r(b) is the gearbox
ratio corresponding to the position b of the gearchange lever,
adimensional; [0026]ρwheels is the radius of the wheels of the
vehicle, in m; [0027]m is the weight of the vehicle, in kg; [0028]g is
the gravitational field on the surface of the Earth, substantially equal
to 9.81 ms-2; and [0029]θtilt is the inclination of the
surface on which the vehicle stands, supplied by the slope sensor, in
rad.

[0030]According to another aspect of the invention, also proposed is a
method for determining a mapping of the torque transmitted by a clutch
fitted to a motor vehicle as a function of the position of a clutch
control member, wherein, while the vehicle is running, said mapping is
updated based on position thresholds of the clutch control member while
the vehicle is running. In addition, during said update, the values of
said thresholds are modified as a function of the minimum and maximum
values of the positions of the control member recorded in said mapping,
and of the current value of said thresholds.

[0031]The invention will be better understood on studying the following
detailed description of a number of embodiments taken as examples that
are in no way limiting and illustrated by the appended drawings in which:

[0032]FIG. 1 is a schematic diagram of a device for determining a mapping
of the torque transmitted by a clutch fitted to a motor vehicle as a
function of the position of a clutch control member, according to one
aspect of the invention; and

[0033]FIG. 2 is a block diagram representing a hill-start assistance
system for a motor vehicle fitted with a device according to FIG. 1.

[0034]FIG. 1 illustrates an example of a device for determining, while the
vehicle is running, a mapping of the torque transmitted by a clutch
fitted to a motor vehicle as a function of the position of a clutch
control member, in this instance a clutch pedal, according to one aspect
of the invention.

[0035]The device 1 comprises a mapping 2 of the torque transmitted by the
clutch fitted to motor vehicles as a function of the position of the
clutch pedal 3 that can be actuated by the driver of the vehicle. The
mapping 2 is included in an electronic control unit 4 and can be stored
in a memory. The electronic control unit 4 comprises a module 5 for
updating the mapping 2. The module 5 for updating the mapping 2 uses
position thresholds of the clutch control member, stored in a first
memory module 6.

[0036]The updating module 5 comprises a computing module 7 making it
possible to modify the values of the position thresholds of the clutch
pedal 3 as a function of the minimum and maximum values of the positions
of the clutch pedal 3 recorded in the clutch mapping 2, and of the
current or actual values of the stored thresholds.

[0037]A counter 8 makes it possible, at any time, to know the number of
complete updates of the mapping 2 that have been carried out since the
vehicle was placed in service, based on a predetermined initial mapping
2. Each time the updating module 5 finishes a complete update of the
mapping 2, the counter 8 is incremented by one unit.

[0038]A comparator 9 compares the current value of the counter 8 with a
predetermined value Nretro stored in a second memory module 10.
Therefore, when Nretro successive updates of the mapping 2 have been
made, the updating module 5 commands the computing module 7 to modify the
values of the thresholds stored in the first memory module 6 as a
function of the minimum and maximum values of the positions of the clutch
pedal 3 recorded in the clutch mapping 2, and of the current value of the
thresholds currently stored in the first memory module 6. The counter 8
is then reset to zero.

[0039]The updating module 5 receives an item of information representative
of the position of the clutch pedal 3 by a sensor 11 via a connection 12.
Moreover, a sensor 13 of the torque transmitted by the clutch delivers to
the updating module 5, via a connection 14, an item of information
representative of the torque transmitted by the clutch. As a variant, the
torque sensor 13 can be replaced by an estimator.

[0040]The position of the clutch pedal θclutch is expressed in
percentages of the maximum travel of the clutch pedal 3. A percentage of
0% corresponds to the clutch completely disengaged, that is to say the
clutch pedal 3 pushed in to the maximum, and a percentage of 100%
corresponds to the clutch completely engaged, that is to say the clutch
pedal 3 completely released. In the mapping 2, the torque values vary
between a minimum torque value and a maximum torque value, and this range
of torque values is divided into a predetermined number of ranges
Nrange. For each of the torque ranges, the device, based on several
values measured in this range, determines an average torque for the range
i:

CCi(θclutch--CC(i), ECTCC(i)).

θclutch--CC(i) represents the average position, in
percentage, of the clutch pedal 3 for the current range i, and
ECTCC(i) represents the average torque in the current range i, in
Nm.

[0041]A top threshold θclutchHB corresponds to a position of
the clutch pedal 3 beyond which the clutch is considered to be engaged,
that is to say transmitting torque; the top threshold may for example be
95% initially. A bottom threshold θclutchLB is a position
threshold of the clutch pedal 3 below which the clutch is considered to
be disengaged, that is to say transmitting no torque, for example equal
to 5% initially. An intermediate position threshold θclutchLB,
relatively close to the top position threshold θclutchHB, is
also used, for example equal to 80% initially.

[0042]In other words, the position thresholds are indexed relative to the
clutch curve learned or updated. The evolution of the position thresholds
must be much slower than the convergence of the estimate of the clutch
mapping 2. For example, the value of the position thresholds can be
updated after Nretro complete updates of the mapping 2, where, for
example, Nretro=30.

[0043]For the bottom position threshold θclutchLB, a bottom
limit θclutchLB lim B and a top limit
θclutchLB--lim H can be imposed so that, at any
time, the following equation is verified:

θclutchLB
limB≦θclutchLB(k)≦θclutchLB--.su-
b.lim H

in which k represents the number of threshold updates made.

[0044]Similarly, for the top position threshold θclutchHB, a
bottom limit θclutchHB lim B and a top limit
θ.sub.clutcHB lim H can be imposed so that, at any time, the
following equation is verified:

[0048]Therefore, every Nretro updates of the clutch mapping 2, the
position thresholds can be updated relative to the minimum value
θclutchCC--min (k) and the maximum value
θclutchCC--max (k) of the clutch mapping 2 so that:

in which:αclutchLB and αclutchHB are factors of
convergence of the thresholds verifying:

{ 0 < α clutchLB ≦ 1 0 < α
clutchHB ≦ 1 ##EQU00005##

and ΔθclutchLB and ΔθclutchHB are
factors of indexation of the position thresholds of the accelerator pedal
3 relative to the clutch curve verifying:

{ 0 < Δθ clutchLB < 100 0 <
Δθ clutchHB < 100 ##EQU00006##

[0051]In a simplified manner, the indexation factors can be considered to
be constants. The intermediate position threshold θclutchMB
can be determined in a simplified manner by the following equation:

θclutchMB(k)=(θclutchHB(k)-θclutchLB(k))*-
0.8+θclutchLB(k)

in which the intermediate position threshold θclutchMB is, for
example, equal to 80% of the range [θclutchLB (k)
θclutchHB (k)].

[0052]To increase the speed of convergence toward the position thresholds
suited to the clutch mapping 2 updated, the convergence factors
αclutchLB, αclutchHB can vary during the use of the
vehicle. During the first retrogrades or the first kilometers of the
vehicle, it is possible to choose high values for the convergence factors
αclutchLB, αclutchHB. For example, it is possible
to choose αclutchLB=1 and αclutchHB=1; therefore,
the clutch curve is learned or updated with constant thresholds;
thereafter it is possible to lower the value in order to quickly suit the
position thresholds to the clutch mapping 2, and finally it is possible
to switch to the default value, lower than but very close to 1, in order
to cause the thresholds to evolve very slowly during the use of the
vehicle.

[0053]FIG. 2 illustrates an example of a system for assisting a hill start
or a hill maneuver of a motor vehicle fitted with a device 1 for
determining a mapping of the torque transmitted by a clutch as
represented in FIG. 1.

[0054]The hill-start assistance system also comprises a control module 17
belonging to the electronic control unit 4 and controlling a braking
device 18 so as to release the brakes during a hill start, via a
connection 19, when the torque transmitted by the clutch compensates for
the effects induced by the slope. The control module 17 comprises a
module 20 for estimating the torque to be supplied by the clutch in order
to overcome the forces of gravity, and a comparator 21 of the torque to
be supplied in order to overcome the forces of gravity and of the torque
supplied by the clutch available in the mapping 2. The control module 17
also comprises a module 22 for determining the gearbox ratio
corresponding to the position b of the gearchange lever.

[0055]Also, the electronic control unit 4 receives an item of information
representative of the slope θtilt from a slope sensor 23, via
a connection 24. The electronic control unit 4 also receives a plurality
of other signals 25 supplied by various sensors or estimators on board
the vehicle. These signals are representative of the value of various
parameters of operation of the vehicle.

[0056]During a hill start or maneuver carried out by the driver of the
vehicle, the estimation module 20 evaluates the torque to be supplied
CTd to the wheels in order to start, via the following relation:

CTd=r(b)ρwheelsmgsin(θtilt)

in which: [0057]CTd represents the torque to be supplied by the
clutch in order to overcome the forces of gravity, in Nm; [0058]r(b)
represents the gearbox ratio corresponding to the position b of the
gearchange lever, adimensional; [0059]ρwheels represents the
radius of the wheels of the vehicle, in m; [0060]m represents the weight
of the vehicle, in kg; [0061]g represents the gravitational field on the
surface of the Earth, equal to 9.81 ms-2; and [0062]θtilt
represents the inclination of the surface on which the vehicle stands,
supplied by the slope sensor, in rad.

[0063]For this computation, the module 22 supplies to the estimation
module 20 the gearbox ratio corresponding to the position b of the
gearchange lever. The comparator 21 compares the torque to be supplied
estimated by the estimation module 20, and the torque supplied by the
clutch the value of which is available in the mapping 2. When the torque
supplied by the clutch is greater than or equal to the torque to be
supplied estimated by the estimation module 20, the control module 17
controls the braking device 18 so as to release the brakes.

[0064]The present invention makes it possible to have a clutch mapping
updated over time taking account of the wear of the clutch, and thus
making it possible to obtain a clutch mapping of enhanced precision.

[0065]The invention also makes it possible to supply assistance to the
driver for a hill start taking account of the wear of the clutch, and
with enhanced precision.